Classifications

• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
  • H10K59/00—Integrated devices, or assemblies of multiple devices, comprising at least one organic light-emitting element covered by group H10K50/00
  • H10K59/10—OLED displays
  • H10K59/12—Active-matrix OLED [AMOLED] displays
• • G—PHYSICS
  • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
  • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
  • G09G3/00—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes
  • G09G3/20—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters
  • G09G3/22—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources
  • G09G3/30—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources using electroluminescent panels
• • G—PHYSICS
  • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
  • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
  • G09G3/00—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes
  • G09G3/20—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters
• • G—PHYSICS
  • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
  • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
  • G09G2300/00—Aspects of the constitution of display devices
  • G09G2300/08—Active matrix structure, i.e. with use of active elements, inclusive of non-linear two terminal elements, in the pixels together with light emitting or modulating elements
  • G09G2300/0809—Several active elements per pixel in active matrix panels
  • G09G2300/0842—Several active elements per pixel in active matrix panels forming a memory circuit, e.g. a dynamic memory with one capacitor
  • G09G2300/0857—Static memory circuit, e.g. flip-flop

Definitions

• the present invention relates to an active matrix display device in which a pixel includes a plurality of divided pixels.
• EL element as a light-emitting element
• EL display devices are classified into passive organic EL display devices and active (active matrix) EL display devices.
• active matrix EL display devices are becoming more popular, in view that higher resolution is achieved by an active matrix EL display device in which a thin film transistor is provided in each pixel and display is controlled.
• An organic EL element is a current-driven element.
• a driving transistor in which the amount of current is controlled according to a data voltage is provided in each pixel.
• difficulty is encountered in inhibiting variation in characteristics of the driving transistors, and allowing an appropriate current to always flow through the driving transistor according to the data voltage.
• the active matrix organic EL panel is driven digitally (see WO 2005-116971). With digital driving, the amount of light emission at each pixel may be maintained constant, and the influences of the characteristic variation of driving transistors can be inhibited.
• one frame period is divided into a plurality of sub-frame periods, and whether or not light is emitted during a sub-frame period having a certain light emission period is controlled. Therefore, the data must be written to the pixel for each sub-frame. Because of this, a frame memory must be provided in order to allow data of one frame to be written in the frame memory and data corresponding to each sub- frame to be read from the frame memory and supplied to each pixel.
• each pixel includes a plurality of divided pixels, wherein each divided pixel has a data storage element and emits light based on supplied data, and amounts of light emission by the divided pixels are weighted, and each bit of data of a plurality of bits for a pixel is supplied to the corresponding divided pixel in which the amount of light emission is correspondingly weighted.
• the amounts of light emission of the divided pixels are weighted by weighting power supply voltages to be supplied to the respective divided pixels.
• the power supply voltage to be supplied to each divided pixel can be switched.
• each of the divided pixels includes a 1-bit static memory as the data storage element.
• each of the divided pixels includes an organic electroluminescence element as a light-emitting element.
• the light emission of the divided pixels can be controlled with grayscale data and a grayscale display can be achieved. Therefore, the frame memory is no longer necessary.
• FIG. 1 A is an equivalent circuit diagram of a divided pixel
• FIG IB is a diagram showing placement and connection of the divided pixel
• FIG 2 A is an equivalent circuit diagram of a pixel
• FIG. 2B is a diagram showing placement and connection of the pixel
• FIG 3 is a diagram showing a current-voltage characteristic of an organic EL element
• FIG. 4 is an overall structural diagram of an organic EL panel
• FIG. 5 is a driving timing chart of the organic EL panel
• FIG 6 is a table showing switching of a power supply voltage setting
• FIG. 7 is an overall structural diagram of an organic EL panel including only P-type transistors.
• FIGS. IA and IB show a structure of a divided pixel circuit in which a static memory is introduced in a pixel circuit.
• FIG. IA is an equivalent circuit diagram of the divided pixel or the like
• FIG IB is a diagram showing placement and connection of the divided pixel circuit as viewed from a side opposite the light emission surface.
• a pixel in FIGS. IA and IB include a first organic electroluminescence ("EL") element 1 which contributes to light emission, a first driving transistor 2 which drives the first organic EL element 1, a second organic EL element 3 which does not contribute to light emission, a second driving transistor 4 which drives the second organic EL element 3, and a gate transistor 5 which controls supply.
• EL organic electroluminescence
• Data voltages are supplied on a data line 7 to a gate terminal of the first driving transistor 2.
• the first driving transistor 2, the second driving transistor 4, and the gate transistor 5 are p-channel transistors.
• An anode of the first organic EL element 1 is connected to a drain terminal of the first driving transistor 2 and to a gate terminal of the second driving transistor 4.
• a gate terminal of the first driving transistor 2 is connected to an anode of the second organic EL element 3, to a drain terminal of the second driving transistor 4, and to a source terminal of the gate transistor 5.
• a gate terminal of the gate transistor 5 is connected to the gate line 6, and the drain terminal of the gate transistor 5 is connected to the data line 7.
• Source terminals of the first driving transistor 2 and the second driving transistor 4 are connected to a power supply line 8
• cathodes of the first organic EL element 1 and the second organic EL element 3 are connected to a cathode electrode 9.
• the gate transistor 5 when the gate line 6 is selected (when the gate line 6 is set at a Low level), the gate transistor 5 is switched ON, and a data voltage supplied on the data line is read into the pixel circuit through the gate transistor 5.
• the first driving transistor 2 When the data voltage is Low, the first driving transistor 2 is switched ON.
• the first driving transistor 2 When the first driving transistor 2 is switched ON, the anode of the first organic EL element 1 is connected to the power supply line 8 on which a power supply voltage VDD is supplied, a current flows through the first organic EL element 1 , and light is emitted.
• the gate terminal of the second driving transistor 4 is also set at VDD, the second driving transistor 4 is switched OFF, and a potential of the anode of the second organic EL element 3 is dropped to a cathode potential VSS. Because the cathode potential VSS is supplied to the gate terminal of the first driving transistor 2, the written data Low continue to be maintained while VDD and VSS are being supplied, even after the gate line 6 is set to High and the gate transistor 5 is switched OFF. When the data voltage is High, the first driving transistor 2 is switched OFF and the potential of the anode of the first organic EL element 1 is dropped to the cathode potential VSS.
• the second driving transistor 4 is switched ON, the anode of the second organic EL element 3 is connected to the power supply line 8 on which the power supply voltage VDD is supplied, and current flows through the second organic EL element 3.
• the anode potential of the second organic EL element 3 is reflected in the gate terminal of the first driving transistor 2, and the gate terminal of the first driving transistor 2 is set to the power supply voltage VDD.
• the second organic EL element 3 can be easily formed by forming the first and second organic EL elements as elements of the same structure and blocking light with a line forming a part of the pixel circuit or with a black matrix so that the light is not emitted to the outside from the light emission surface.
• the second organic EL element 3 does not contribute to light emission, it is preferable to place and connect the second organic EL element 3 with a small area so that a large light emission area can be secured for the first organic EL element 1 which emits light, as shown in FIG IB.
• FIGS. 2 A and 2B show an example structure in which a pixel for one color includes three divided pixels 10-0, 10-1, and 10-2. More specifically, the divided pixels 10-0, 10-1, and 10-2 are pixels of the colors, and each of pixels of, for example, R (red), G (green), B (blue), and W (white) includes three divided pixels as shown in FIGS. 2 A and 2B.
• FIG 2 A is an equivalent circuit diagram
• FIG. 2B is a diagram of placement and connection as viewed from a side opposite the light emission surface.
• power supply lines 8-0, 8-1, and 8-2 are placed, and power supply voltages VO, Vl, and V2 are supplied to the power supply lines 8-0, 8-1, and 8-2, which are determined by a current- voltage characteristic diagram of the organic EL element shown in FIG 3.
• the power supply voltages VO, Vl, and V2 are voltages which are determined such that a ratio among currents 10, II, and 12 to be supplied through the organic EL elements of the divided pixels 10-0, 10-1, and 10-2, respectively, is 1 :2:4.
• the organic EL elements are switched ON by data voltages supplied to the divided pixels 10-0, 10-1, and 10-2, 8 different light emission intensities can be obtained.
• gate line 6-0 is sequentially selected and Low data are written in the divided pixel 10-0
• the gate line 6-1 is then selected and High data are written to the divided pixel 10-1
• the gate line 6-2 is then selected and Low data are written to the divided pixel 10-2
• the divided pixel 10-0 is switched ON
• the divided pixel 10-1 is switched OFF
• the divided pixel 10-2 is switched ON.
• FIG 4 shows an overall structure of a single-color active matrix organic EL panel of n rows and m columns
• FIG. 5 shows a driving timing chart of the active matrix organic EL panel.
• 3-bit data are input to inputs XO (bit 0), Xl (bit 1), and X2 (bit 2) of a data driver 11.
• XO bits 0
• Xl bits 1
• X2 bits 2
• a dot clock DCLK (not shown in FIG 4) is input to the data driver 11, data of one line are sequentially read to a shift register 13 storing data of each bit.
• the 3 -bit data of one line read into the shift register 13 are reflected in the data line 7 by a multiplexer 14 which controls an output of the read 3-bit data and enable lines EXO, EXl, and EX2.
• bit 0 is output to the data line 7 if the enable line EXO is selected
• bit 1 is output to the data line 7 if the enable line EXl is selected
• bit 2 is output to the data line 7 if the enable line EX2 is selected.
• selection data (in the example configuration, High) are input to an input Y of a gate driver 12, and are subsequently read into a shift register 15.
• the shift register 15 sequentially transfers the selection data with a vertical transfer clock. Normally, of the shift register 15 of n lines, selection data (High) are stored only in the register of one line and this line is selected.
• an enable line EYO is selected on a kth line storing the selection data of the shift register 15
• the divided pixel 10-0 of the kth line is selected and data of bit 0 supplied to the data line 7 are written to the divided pixel 10-0 of the kth line.
• the data driver 11 and the gate driver 12 can be formed on a same glass substrate by using a high-performance transistor such as low temperature polysilicon, and, thus, cost can be further reduced.
• the circuit of the divided pixel does not need to be the structure shown in FIGS. IA and IB having a static memory.
• the voltages VO, Vl, and V2 to be supplied to the power supply lines 8-0, 8-1, and 8-2 may be switched at a suitable period.
• a combination A of the voltage VO to the power supply line 8-0, the voltage Vl to the power supply line 8-1, and the voltage V2 to the power supply line 8-2; a combination B of the voltage V2 to the power supply line 8-0, the voltage VO to the power supply line 8-1 , and the voltage Vl to the power supply line 8-2; and a combination C of the voltage Vl to the power supply line Vl , the voltage V2 to the power supply line V2, and the voltage VO to the power supply line 8-2 can be alternately switched at a certain timing, and the enable lines may be selected corresponding to the switched combination, hi this manner, it is possible to write bit data to the divided pixels indicating light emission intensities corresponding to the bit data without a contradiction.
• the data of bit 0 are written to the divided pixel 10-1 having a power supply voltage of VO supplied to the power supply line 8-1 by selection of EXO and EYl
• the data of bit 1 are written to the divided pixel 10-2 having a power supply voltage of Vl supplied to the power supply line 8-2 by the selection of EXl and EY2
• the data of bit 2 are written to the divided pixel 10-0 having a power supply voltage of V2 supplied to the power supply line 8-0 by the selection of EX2 and EYO.
• the data of bit 0 are written to the divided pixel 10-2 having a power supply voltage of VO supplied to the power supply line 8-2 by selection of EXO and EY2
• the data of bit 1 are written to the divided pixel 10-0 having a power supply voltage of Vl supplied to the power supply line 8-0 by selection of EXl and EYO
• the data of bit 2 are written to the divided pixel 10-1 having a power supply voltage of V2 supplied to the power supply line 8-1 by selection of EX2 and EYl.
• the voltages applied to the divided pixels can be made uniform and the degradation of the organic EL element can be averaged.
• Such a structure can be achieved by providing a switch which can be switched according to a signal indicating the selection of the combinations A, B, and C and switching so as to select which of the voltages VO, Vl, and V2 is to be supplied to which of the power supply lines 8-0, 8-1, and 8-2.
• the data driver 11 and the gate driver 12 are realized as a driver IC and other pixel circuits, and a selector 16 which selects and outputs an output of the gate driver 12 to the gate line 6, and a selector 17 which selects and outputs a voltage Voff for setting the gate transistor 5 not selected to the gate line 6 are formed by P-type transistors.
• the organic EL panel is constructed with only P-type transistors in this manner, the cost can be further reduced, and a higher resolution which requires a higher speed operation and a larger size which requires a higher driving power can be easily realized.

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• Engineering & Computer Science (AREA)
• Physics & Mathematics (AREA)
• Computer Hardware Design (AREA)
• General Physics & Mathematics (AREA)
• Theoretical Computer Science (AREA)
• Microelectronics & Electronic Packaging (AREA)
• Control Of Indicators Other Than Cathode Ray Tubes (AREA)
• Control Of El Displays (AREA)
• Electroluminescent Light Sources (AREA)

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• 2007
  • 2007-01-23 JP JP2007012895A patent/JP2008180802A/ja active Pending
• 2008
  • 2008-01-08 KR KR1020097015398A patent/KR20090107509A/ko not_active Application Discontinuation
  • 2008-01-08 WO PCT/US2008/000267 patent/WO2008091492A2/en active Application Filing
  • 2008-01-08 EP EP08705533A patent/EP2126975A2/en not_active Withdrawn
  • 2008-01-08 US US12/522,397 patent/US20100085388A1/en not_active Abandoned

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